(172e) Large-Scale Coupled CFD-DEM Simulations of Fluidized Granular Systems

Granular flows are characteristic to numerous natural phenomena and are part of many processes of the pharmaceutical and chemical industries. In these industrial processes granular flows have a critical impact on the product’s performance and safety. For example, in continuous powder blending of active pharmaceutical ingredients (APIs) and excipients prior to tableting, the granular flow properties of the components determine the content uniformity of the tablets made later in the process. Only a detailed understanding of the influence of particle size, shape, surface texture and other properties on the mean and the fluctuating flow fields in granular flows allows a precise design and optimization of this manufacturing operation.

In recent years Discrete Element Model (DEM) simulations have increasingly been used to study flows of granular systems. In the pharmaceutical and other industries, fine granular materials are encountered (typically in the order of ten to several hundred microns), where both particle-particle interactions and fluid drag have significant contributions. Examples include fluid-bed drying, hopper filling/discharge, chute flows, die filling or coating processes. Thus, accounting for fluid-particle interaction it is necessary to correctly describe such processes, and to design and to scale-up industrial devices.

Combining Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM) allows simulating fluidic-granular systems. The main advantage of CFD–DEM is that detailed particle-scale information is obtained, including particle trajectories and forces acting on individual particles. The coupling of CFD and DEM is realized through a fully two-way particle–fluid interaction forces, where the high-performance GPU-based DEM code and the CFD code (AVL-Fire®) are coupled. The advantage of our CFD–DEM hybrid CPU/GPU simulation method is, that the codes runs inside a single workstation but on separate computing platforms. We are able, to do simulations for up to 25 million particles.

The numerical results of fluidized beds obtained in this work were validated against experimental data. The experimental and CFD–DEM simulation data include profiles of the time averaged vertical particle velocity and time-averaged particle velocity fields. The results of our work show excellent agreement with the experimental data.

Our application of the validated code is the simulation of a bottom-spray Wurster-Coater. Air streams into the device through a diffusor plate at the bottom, which consists of regions with different porosities. The plate has larger orifices below the Wurster draft tube and therefore the fluidization gas enters at higher velocity below the tube. Particle coating evolution and residence time distribution is studied for a coating process of several million particles.